Radiation detector for insertion into a blood vessel

ABSTRACT

A radiation detector for medical use to be inserted into the blood vessel is provided with a blood channel disposed in parallel with the blood flow. A semiconductor element is placed in the blood channel to detect the radiations from the radioisotope introduced into the blood vessel, with the radiation-receiving face thereof exposed to the interior of the blood channel.

United States Patent I I I Inventors Tetsuji Kohayashi YokoItama-shi;

Tekayanagi Seiiehi, Tokyo, both of, Japan 666,594

Sept. II, 1967 Aug. 10, 197i Tokyo Shibaun Electric Co., Ltd.Kawasaki-ski, Japan Appl. No. Filed Patented Assignee RADIATION DETECTORFOR INSER'I'ION INTO A BLOOD VISSEL 10 Claims, 9 Drawing Figs.

[15. CL 128/205 F, 73/l94 E, 250/435 MR, 250/83 R Int. Cl Afilb 5/02FieldofSearch 128/2, 2.05,

2.05 D, 2.05 F, 2.05 M, 2.05 P, 2.05 T, 2.l; 250/435 FC, I06 T, 83, 83.3

[56] References Cited UNITED STATES PATENTS 3,427,454 2/l969 Webb .7128/2.l X

OTHER REFERENCES IRE Transactions On Medical Electronics, Dec. 1959,pages 228 229, 230, 231 relied on; copy in Group 280, 73/194 (E.M.)

Primary ExaminerAnton O. Oechsle Assistant Examiner-Marvin SiskindAttorney-Stephen ll. Frishauf ABSTRACT A radiation detector for medicaluse to be inserted into the blood vessel is provided with a bloodchannel disposed in parallel with the blood flow. A semiconductorelement is placed in the blood channel to detect the radiations from theradioisotope introduced into the blood vessel, with theradiation-receiving face thereof exposed to the interior of the bloodchannel.

PATENTEUAUGIOIH?! 3.598.109

FIG. 6;

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s elm mum/64 6 INVEgVIOR; M4.

RADIATION DETECTOR FOR INSERTION INTO A BLOOD VESSEL BACKGROUND OF THEINVENTION The present invention relates to an apparatus for detectingthe radiations emitted from the radioisotopes purposely introduced intothe blood of a living body by being fixedly inserted into the prescribedposition of the blood vessel.

In recent years, due to advance in nuclear medicine, approaches havebeen made to the diagnosis of the functions of various organs containedin a living body by introducing in advance into the interior thereofappropriate doses of radioisotopes harmless to the living body, andmeasuring the radiations from said radioisotopes by means of a radiationdetector located at the prescribed position within the living body.Among these methods there is one which comprises introducingradioisotopes into the blood and determining the radiations therefromwithin the blood vessel.

Detailed description will now be given of this procedure. First,radioisotopes of, for example, iodine, potassium and krypton arepurposely taken into the blood vessel from an appropriate part of theliving body, and the radiations from the radioisotope carried along withthe blood is determined by a radiation detector disposed at a pointwithin the blood vessel spaced from the place where said radioisotope isinitially introduced. These determinations are used in checking theevidence of abnormal developments in the function of organs such as theheart and liver by ascertaining the speed and condition of bloodcirculation and the extent of absorption in the living body of theradioisotope thus introduced. What is the most important in suchdiagnosis is the accurate and definite measurement of the radiationspresent in the blood vessel. If mere detection of the evidence ofradiations is all that is required, then it may be contemplated to usethe Geiger- Muller counter (GM counter) as commonly called. However,this device requires a high operating voltage of 300 to 400 v., that itis not only incapable of being substantially miniaturized but also ofshort life, thus presenting extreme difficulties in inserting it intothe blood vessel ofthe living body.

For the foregoing reason, use has begun to be made of a compactsemiconductor radiation detector requiring only a low-operating voltage.This semiconductor device is characterized in that it is compact andrigid and only requires as low an operating voltage as about to 30 v. orless, so that it is seemed to be a very excellent radiation detector formedical use. However, unlike other purposes, the medical application forwhich the present invention is intended dictates that the semiconductorradiation detector to be used in the blood vessel, be of as compactconstruction as possible, extremely sensitive to radiations and also befree from appreciably disturbing the blood circulation when insertedinto the blood vessel. However, mere miniaturization of thesemiconductor detector will not serve the purpose, because the closeattachment of the inner wall of the blood vessel to the outercircumferential surface of the detector causes the natural blood flow tobe obstructed and delayed. In other words, the volume ofthe detectoritself gives rise to an unnatural blood flow in the vessel, eventuallypresenting difficulties in final diagnosis. In some cases, the insertionof such detector may completely block the blood flow, exposing life tosubstantial danger. The smaller the inner diameter of the blood vesselthus affected, the more prominent will be this tendency. Furthermore,unless aided by any appropriate additional device, mere miniaturizationof the prior art semiconductor detector would only serve to reduce theradiationsensitive area, i.e., the sensitive face where radiations areto be detected, with the resultant degradation of detecting efficiency.Due to the aforementioned unsolved problems, the commonly used radiationdetector has been in capable of offering satisfactory performance wheninserted into the blood vesseljust as it is produced.

SUMMARY OF THE INVENTION It is accordingly an objectof the presentinvention to provide a radiation detector for medical use which, wheninserted into the blood vessel, is not likely to disturb or block theblood circulation.

Another object of the present invention is to offer a radiation detectorfor medical use which will not affect the blood flow, even when it isinserted into a relatively narrow blood vessel to cause part of theouter circumferential surface thereof to be closely attached to theinner wall of the blood vessel.

A further object of the present invention is to offer a radiationdetector for medical use which displays a sufficient detectingefficiency, even though it may be miniaturized as far as possible.

These and other objects and advantages of the present invention will bemore fully understood by reference to the fol- .lowing detaileddescription of certain preferred embodiments thereof in connection withwhich reference may be had to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows the condition in whichthe radiation detector of the present invention is disposed in the bloodvessel;

FIG. 2 is a slantwise perspective of the radiation detector for medicaluse according to one embodiment of the present invention;

FIG. 3 is a particularly enlarged slantwise view of the semiconductorelement used in the radiation detector of FIG. .2; l FIGS. 4A and 4B areslantwise perspective views of the ;radiation detector according toanother embodiment of the present invention, FIG. 4A mainly illustratingthe upper side land FIG. 4B the lower side; and

FIGS. 5 to 8 respectively show slantwise views of the radiationdetectors according to other embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION l Referring now to theaccompanying drawings, more particularly to FIG. 1, the apparatus 1 ofthe present invention is placed in the prescribed blood vessel 2 of aliving body by i being fitted to the end of a catheter-type guide cord3, which comprises a conductor covered with insulation or enclosed in aninsulating tube. While, in this case, the living body may represent thatofeither a human being or animal, the following description will solelydeal with the human being by way of simplification of explanation. Theblood vessel 2 is, for example, a venous tube in the arm or an arterialtube near the inlet to the liver, the inner diameter of these tubesbeing about 2 to 3 mm. Radioisotopes such as P and K are introduced fromother blood vessels connected to said blood vessel 2. Theseradioisotopes are carried through the blood vessel 2 along with theblood. While they are passing therethrough, their radiations aredetermined by the radiation detector I for medical use positionedtherein, the circumferential wall 9 of which is generally close or incontact with the inner wall 8 of the blood vessel 2. As described later.the radiation detector I is provided with a radiation-sensitive areacomprising a semiconductor element, so that the detector can measure theradiations of the radioisotope entering the radiation-sensitive area. Ofcourse, the detector I is supplied with bias voltage, and the detectionoutput is taken outside of the living body. For this purpose, the guidecord 3 has coaxial conductors 4, 4 enclosed therein. One end of theguide cord 3 containing these conductors 4, 4 is connected to thesemiconductor element' and the other end thereof is led outside of theblood vessel 2, namely, the living body. Connected to said other end isa source 5 to supply the conductors with bias voltage. The radiationdetection outputs from the detector I are presented in the form ofvoltage variations between the conductors 4-4 or variations in thecurrent passing through the system. The outputs or variations aremeasured by an electric output measuring section 6. Thus this outputmeasuring unit is constructed in such a manner that the electric output,for example, from the output resistor 7 connected as shown is measuredand indicated by an instrument (not shown) such as an indicator. Thisarrangement makes it possible to find the time required for the bloodflow to run from the place where the radioisotope is initiallyintroduced to the point at which the detector 1 is positioned, namely,the speed of blood circulation, or to ascertain the absorption of theradioisotope in transit through the blood vessel, thus eventuallycarrying out the diagnosis of the function of the desired organs such asthe heart and liver contained in the living body. As previouslymentioned, to check the natural condition of the living body, thedetector 1 is of such construction as to permit the accurate anddefinite determination of radiations from the radioisotope introducedtherein without disturbing or obstructing the natural blood flow.

The construction of a radiation detection 1 for medical use according toone embodiment of the present invention will now be described byreference to FIG. 2. In the different drawings appended, like parts aredenoted by like reference numerals. In FIG. 2, the detector 1 consistsof a semiconductor l and a supporter (or holder) ll thereof. Thesupporter 11 is composed of such material as plastics and the like, andis in a columnar form, about 2 mm. in diameter and 5 mm. high. Wheninserted into the blood vessel 2 as shown in FIG. I, the supporter 11has its outer circumferential surface '9 disposed adjacent to the innerwall 8 of the blood vessel 2. Perforated throughout the inside of thecircumferential wall section 9, namely, the central part of thesupporter 11 is an opening having a rectangular cross section, theshorter side being about 1 mm. to define a blood channel 12 therein.When the detector is inserted into the blood vessel 2 in a manner tobring the circumferential wall section 9 of the former in contact withthe inner wall 8 of the latter, the blood channel 12 is aligned with thelengthwise direction of he blood vessel 2. Said lengthwise direction ofthe blood vessel 2 substantially corresponds with the direction of bloodflow as indicated by the broken line arrow D of FIG. 1. Fitted to a partof the inner wall 8 of the blood vessel 2 surrounding the blood channel12 of the detector l is a semiconductor element in the form of a thinrectangular sheet with its radiation-sensitive area 13 exposed at thetop. It will be noted that the radiation-sensitive area 13 as used inthis specification means the surface of a semiconductor which is capableof detecting the radiations from the radioisotope introduced into theblood vessel 2. The rectangular dimensions of the semiconductor elementare such that the shorter side is about 1 mm. and the longer side isabout 3 mm., its thickness being less than 0.2 mm. The semiconductor 10may consist ofsilicon, germanium, gallium arsenide, etc. However, sincea germanium diode has high magnitude to the reverse saturation currentarising from the reverse bias voltage and gallium arsenide is relativelycostly, silicon is preferred in practical application. The semiconductorelement may be a type having one or more P-N junctions or a nonjunctiontype of extremely high resistivity with an inherent resistivity of aboutl0"Q-cm. However, where a P-N junction type semiconductor is used, theP-N junction 14 will be formed in such a manner that it is disposed inparallel with the surface of the semiconductor It), that is, theradiation-sensitive are 13 thereof. In other words, the l N junction Mwill be aligned in parallel with the axis of the columnar supporter ll.The ex posed portion of said P-N junction [4 will be protected withsilicon dioxide film (not shown). The semiconductor l0 itself may be ofthe mesa type, planar type or other type.

The material ofthe supporter ll may be selected suitably in accordancewith the type of radiations which it is desired to detect by thedetector 1 as a whole. For instance, where the gamma rays are the majorradiations requiring detection, the supporter ll may be composed ofmetals or synthetic resins. And where it is desired mainly to check thebeta rays, the supporter 11 may consist of synthetic resins containingpowders of heavy metals such as lead and cadmium.

The bias voltage to be applied on the semiconductor element 10 isgenerally of the order of less than about 35 volts. The impression ofthe bias voltage may be carried out by connecting one end of the guidecord 3 containing the coaxial conductors 4-4 to the semiconductor 10 byan ohmic contact. The conductors 4-4 coated with insulation constitutethe guide cord 3. The end of said guide cord 3 opposite to that endwhich contacts the semiconductor 10 is connected to the aforesaid source5 of bias voltage so as to apply an appropriate degree of bias voltageon the semiconductor 10. Upon such impression, the radiation enteringthrough the radiation-sensitive area 13 cause pairs of electrons andpositive holes to be produced within the semiconductor 10 in accordancewith the doses of radiations thus introduced, thereby allowing anelectric current as a detection output to flow through the conductors4-4. This detection output appears more prominently when thesemiconductor 10 is a P-N junction type than when it is a nonjunctiontype. The detection output obtained is conducted outside of the bloodvessel 2 through the conductors 4-4 and measured by an output measuringsection 6.

The guide cord 3 holds the conductors in an electrically insulatedrelationship with respect to the inner wall of the blood vessel 2 andhas an adequate degree of rigidity due to the inclusion of theconductors. Therefore, the cord acts as a guide in introducing thedetector 1 into the blood'vessel 2 by fitting it to the end of said cord3.

A description will now be given of the practical operation of theradiation detector l for medical use having the aforementionedconstruction. As shown in FIG. I, the prescribed blood vessel 2 ispartially broken away and a radiation detector 1 is introduced throughthis part and the guide cord 3 integrally fitted thereto is forced inuntil the detector 1 reaches an appropriate depth in the blood vessel 2.The semiconductor element ll] of the detector 1 is impressed in advancewith bias voltage from a bias voltage source S. Then radioisotopes aretaken into the blood vessel 2 at a point spaced from the place where thedetector is positioned. Needless to say, the blood streams run throughthe blood vessel 2 at a pressure of about to I00 mm. Hg. However, sincethe detector 1 of the present invention has a blood channel 12perforated throughout in parallel with the blood vessel 2, namely, inthe direction of blood circulation, this permits the blood to flowthrough the channel 12 freely without any interruption even though theouter circumferential surface 9 of the detector 1 may closely touch theinner wall 8 of the blood vessel 2. While the inner diameter of theblood channel 12 is slightly smaller than the original diameter of theblood vessel 2, the blood flows under pressure as described above, sothat it runs through said blood channel 12 under almost naturalconditions without being obstructed, provided the channel 12 isperforated with a certain diameter in the form of an opening penetratingthroughout the detector in parallel with the blood flow.

Thus when a radioisotope carried along with this natural blood flowreaches the detector 1, the radiation-sensitive area [3 of thesemiconductor 10 thereof disposed along the lengthwise direction of theblood vessel 2 definitely detects radiations from the radioisotope.While the most prominent characteristic of the apparatus according tothe present inven' tion is the provision of a blood channel II in thedetector I it self, the additional advantage is that theradiation-scnsitivc area l3 of the semiconductor element 10 positionedin pumllel with the lengthwise direction of the blood vessel 2 offers anextremely high detecting efficiency. The inventors conducted experimentsvarying the angles which the radiation-sensitive area [3 of thesemiconductor l0 bears to the blood flow. As a result it has beenconfirmed that a parallel arrangement of the radiation-sensitive areaII! with the blood flow, namely, the lengthwise direction of the bloodvessel 2 offered a maximum detecting efficiency. For example, thisarrangement increased the detecting efficiency more than about If) timesover the case where the radiation-sensitive area 13 was disposedperpendicular to the lengthwise direction of the blood vessel 2. Whilethe reason for this result still remains to be seen, it may be explainedby assuming that the parallel arrangement of the radiation-sensitivearea 13 with the lengthwise direction of the blood vessel 2 will help toextend the area of said area contacting the blood and/or the duration ofsuch contact. In either case, the advantage is that the paralleldisposition will considerably elevate the detecting efficiency, eventhough the semiconductor element and consequently the radiationsensitivearea 13 may be reduced in size.

The aforementioned radiation-sensitive area 13, i.e., the surface of thesemiconductor element 10 is shown as coming in direct contact with theblood. However, the radiation-sensitive area 13 may be coated with athin radiation-permeable film, for example, a mica sheet to effectindirect contact with the blood through such sheet. It is to beunderstood, therefore, that while the radiation-sensitive area 13 asused in this specification, of course, means the surface of thesemiconductor element 10 as described above, it also includes thesurface coated with a radiation-permeable substance.

Another embodiment of the present invention which has further increasedthe radiation detecting efficiency will now be described by reference toFIG. 4. As previously noted, the same parts of FIG. 4 as those of FIG. 2are denoted by the same numerals. The radiation detector 1 illustratedin FIG. 4 is characterized in that the inside of the outercircumferential wall section 9 of the supporter I1 is penetrated by ablood channel opening 12 having a triangular cross section and that theinner wall of each of the three sides of the channel 12 is fitted withthe components 101, 102 and 103, which respectively correspond tosemiconductor elements 10. In other words, the blood channel 12 isformed in a manner to be surrounded by the radiation-sensitive areas131, 132 and 133 of the aforementioned components 101, 102 and 103. Ofcourse, connected to the semiconductor components 101, 102 and 103 areconductors 4-4-4 in a manner as shown in FIG. 48 so as to apply theprescribed bias voltage on each of the eomponents. As in the precedingembodiments, the radiation detector 1 thus constructed is inserted intothe blood vessel 2 by being fitted to one end of the guide cord 3containing the triple conductor 4-4-4 to supply bias voltage. Then theblood flows freely through the blood channel 12, though the outercircumferential wall section 9 of the supporter 11 may be tightlyattached to the inner wall 8 of the blood vessel 2 and at the same timeradiations from the radioisotope carried along with the blood aredetected by the aforementioned semiconductor three components 101, 102and 103. Experiments show that this embodiment displayed such goodperformance as offering a detecting efficiency more than twice as highas that of the type of detector shown in FIG. 2.

The blood channel 12 involved in each of the embodiments so fardescribed is perforated in the form of a circumferentially continuousopening. As shown in FIG. 5, however, this channel may be formed in apartially broken away type. The detector 1 of this figure will now bedescribed. The detector 1 similarly consists of a semiconductor element10 and a supporter 11, and the blood channel 12 is formed from curvedplatelike protuberances projecting integrally from the support 11. Firstfitted to a flat surface 16 of the columnar supporter 11 having asemicircular cross section is a semiconductor element 10 with theradiation-sensitive area 13 thereof disposed on the surface. Theintegrally from both ends of the supporter 11 there are projected a pairof curved platelike protuberances 15-15. These protuberances enclose theradiation-sensitive area 13, so that when the semiconductor assembly isinserted into the blood vessel 2, the radiation-sensitive area 13thereof is prevented from directly contacting the inner wall 8 of theblood vessel 2. Defined by the surface of the radiation-sensitive area13 and the inner walls of the protuberances 15-15 projecting from thesupporter 11 is a blood channel 12 in the axial direction of thesupporter 11. Between the ends of the protuberances 15-15 there isformed a gap. However, when the entire detector 1 is inserted into theblood vessel 2, the circumferential surface 9 of the supporter 11 iscontacted with the inner wall 8 of the blood vessel 2 to have this gapplugged therewith. Thus essentially, the partially broken away bloodchannel 12 constitutes a circumferentially continuous penetratingopening, thereby allowing the blood to flow therethrough without anydifficulties. As in the preceding embodiments, the semiconductor element10 is connected to one end of the guide cord 3 containing conductor 4-4.When the semiconductor assembly is inserted into the blood vessel 2 theradiation-sensitive area 13 thereof is disposed in parallel with thelengthwise direction of the blood vessel 2 as is the case with theforegoing embodiments.

Reference is now made to FIGS. 6, 7 and 8. These Figures respectivelyrepresent the embodiments wherein the radiation detector 1 consists of asemiconductor alone without a supporter and a blood channel 12 isprovided within the semiconductor element itself. The detector 1 of FIG.6 will first be described. A semiconductor element body 17 about 3 mm.in outer diameter and 2 mm. high is fabricated by processing a P- typesingle crystal silicon wafer by supersonicor other machining means.Perforated throughout the central part of the semiconductor element body17 is a circular opening 12 about 1 mm. in inner diameter. When, afterordinary chemical treatment of the semiconductor body 17, an N-typelayer 18 is formed at least on the top of the semiconductor body 17 bydiffusing, for example, phosphorus, then there will be created a P-Njunction 14. The upper surface of the N-type layer 18 is used as theradiation-sensitive area 13 to receive radiations from the radioisotopeintroduced. The exposed part of the P- N junction 14 is protected by asilicon dioxide film (not shown). The aforementioned circular opening 12is disposed inside of the circumferential wall section 9 of thesemiconductor element body 17 to constitute a blood channel 12.Connected to the P-type body 17 and the N-type layer 18 of thesemiconductor element respectively are conductors 4-4 by ohmic contact.The coaxial extensions of these conductors 4-4 are inserted into theguide cord 3, which concurrently acts as a guide in introducing theradiation detector into the blood vessel 2. The external contour of thesemiconductor element body is not always required to be cylindrical. Thedetector of the aforesaid construction is used in a relatively fineblood vessel 2. Even though the outer circumferential wall section 9 ofthe semiconductor element body 17 is closely attached to the inner wall8 of the blood vessel 2. The blood isallowed to run freely through theaforesaid blood channel 12, a penetrating opening perforated inside ofsaid circumferential wall section 9 of the semiconductor element bodyitself. Where the detector of FIG. 6 is actually inserted into the bloodvessel 2, it is preferably disposed in such a manner that thecircumferential wall section 9 is placed along the inner wall 8 of theblood vessel 2 and that the blood flowing toward the detector firstdirectly contact the radiation-sensitive area 13. Thus the blood firsttouches the radiation-sensitive area 13, allowing the radiations fromthe radioisotope carried along with the blood to be detectedimmediately. After passing through the blood channel 12, the blood flowcontinues its course as quickly as before in the direction of the bloodflow. In this case, the radiation-sensitive area 13 is disposedperpendicular to the lengthwise direction of the blood vessel so thatthe radiation detecting efficieney is slightly lower than in the for;going embodiments. However, the radiation detector according to theembodiment of FIG. 6 has excellent directivity, because itsradiation-sensitive area 13 is positioned at the foremost end and so isthus capable of checking the incident direction ofthe radiations.

If a semiconductor element is an extremely small columnar body less thanabout 2 mm. in diameter, it will sometimes be difficult to perforate ahole throughout the central part thereof. The only requirement in suchcase would be, as shown in FIGS. 7 and 8, to cut out a part of thesemiconductor element body throughout the entire length inwardly fromthe circumferential wall section, and use the resultant cavity orcavities as a blood channel. More concretely, some portions of theinside of the circumferential wall section of the P-type columnarsilicon semiconductor element body 17 are broken away to form a groovedblood channel or channels 12 in such a manner that the upper and lowersurfaces of thesemiconductor element body I7 thus cut have a flatcrescent plane or a combination thereof as illustrated in FIG. 8. Nextthe top surface of the semiconductor element body 17 is coated with anoxide film of silicon dioxide, and this film, except that on thecircumferential edge section, is removed in the following step. 'lhenphosphorus is.diffused by a known process through illllllli innersurface of the circumferential edge section to form a junction ofplanar-type construction, using the surface thereof as aradiation-sensitive area 13. With the P-N junction as a border line,conductors 4-4 are connected to the P type and N-type regionsrespectively of the semiconductor element body 17. The impression ofbias voltage on these conductors 4-4 radioisotope the withdrawal ofdetection outputs therefrom are carried out mechanical the same manneras in the preceding embodiments. When the detector 1 thus constructed isinserted into the blood vessel 2 by means of a guide cord 3 as shown inFIG. I the blood will flow through a grooved blood channel 12 perforatedinside of the outer circumferential wall section 9 of the semiconductorelement body 17, so that the natural blood streams will not interrupted.The radiation-sensitive area 13 formed in the aforementioned mannerdetects radiations from the radioisotope introduced into the bloodvessel 2. For increasing the mechaNical strength of the semiconductorelement body 17, it is permissible to coat the outer circumferentialwall section 9 thereof with reinforcing material or to fit thesemiconductor element body 17 itself tightly into a cylindrical metalsleeve. Also the plane of P-N junctions, namely, the radiation-sensitivearea l3 may be located on the arched inner surface 19 of thc groovedblood channel 12.

FIG. 8 illustrates a semiconductor radiation detector wherein groovedblood channels 12 are formed by cutting out three parts of the inside ofthe circumferential wall section of the semiconductor element body 17contacting the inner wall of the blood vessel. The parts of the detectorshown in FIG. 8 which corresponds to those of the foregoing figures aredenoted by the same reference numerals and a detailed descriptionthereof is omitted here. The increased blood channels 121I23 asillustrated in FIG. 8 will ensure the freer flow of the blood throughthe detector assembly. Thus when the detector is inserted into the bloodvessel 2 as shown in FIG. 1, the blood will flow through the three bloodchannels 121 122 and 123, thus allowing the blood to flow in a morenatural condition than is possible with the foregoing embodiments. Inthis case, too, the detection of radiations is effected by theradiation-sensitive area I3. However, if said face 13 is providcd on theinner surface 19 of each of the three blood channels I21, I22 and 123,then the detecting efficiency will be more improved.

As described above, the radiation detector of the present inventionenables the radiations from the radioisotope introduced into the bloodvessel to be determined accurately without interrupting the blood flowdue to the provision of a blood channel having a certain cross-sectionalarea. even when the detector is inserted into a relatively narrow bloodvessel. Since the parallel arrangement of a radiation-sensitive areawith the lengthwise direction of the blood vessel offers a higherdetecting efficiency, the detector can be considerably reduced in sizeby using a small semiconductor element.

It will be evident from the foregoing description that manymodifications and variations are feasible in the light of theaforementioned techniques.

We claim:

I. A radiation detector for medical use adapted to be inserted into ablood vessel comprising: a guide cord including conductors enclosedtherein; a source of bias voltage coupled to said conductors; adetection member coupled to said guide cord and having an outercircumferential wall section and a blood channel formed in said wallsection extending in a direction longitudinally of said member andsubstantially parallel with the lengthwise direction of the blood vesselinto which said detection member is adapted to be inserted,

whereby, upon insertion of said member into a blood vessel,

blood may flow through said blood channel,

said detection member including a semiconductor element coupled to saidbias voltage via said conductors and having a radiation-sensitive area,said semiconductor element being disposed such that saidradiation-sensitive ares directly contacts with blood flowing throughsaid blood channel, the radiation emitted from the blood flowing throughsaid blood channel being detected by said semiconductor element.

2. A radiation detector according to claim 1 wherein said semiconductorelement has P N junction and said radiationsensitive area is disposedadjacent to and along a surface of said semiconductor element.

3. A radiation detector for medical use according to claim 2 wherein thesurface of the radiation-sensitive area is positioned substantially inparallel with the lengthwise direction of said blood channel, anddirectly contacts blood flowing through said blood channel.

4. A radiation detector according to claim I wherein the outer surfaceof the wall section of said detection member is dimensioned to contactthe inner wall of the blood vessel into which it is adapted to beinserted.

5. A radiation detector according to claim I wherein said detectionmember includes a support member having said blood channel formedtherein and wherein said semiconductor element is disposed within saidblood channel and is supported by said support member so that saidradiation-sensitive area directly contacts blood flowing through saidblood channel.

6. A radiation detector according to claim 5 wherein said semiconductorelement comprises a rectangular thin semiconductor element having a P-Njunction formed substantially adjacent to and in parallel with thesurface thereof, the radiation-sensitive area of said semiconductorelement being the surface thereof parallel to said P-N junction, saidsemiconductor element being positioned so that said radiation-sensitivearea is substantially in parallel with the lengthwise direction of saidblood channel.

7. A radiation detector according to claim 1 wherein the outercircumferential wall section of said detection member is formed by saidsemiconductor element and said blood channel is formed in thesemiconductor element itself, the outer surface of said wall sectionbeing dimensioned to contact the inner wall of the blood vessel intowhich said detection member is adapted to be inserted.

8. A radiation detector according to claim 7 wherein saidradiation-sensitive area is disposed substantially perpendicular to thelengthwise direction of said blood channel and directly contacts bloodflowing through said blood channel.

9. A radiation detector for medical use according to claim 7 whereinsaid blood channel is a grooved channel formed by cutting out a part ofthe semiconductor element body inwardly from the outer circumferentialwall section thereof, said radiationsensitive area comprising thesurface of the semiconductor element body disposed adjacent to and inparallel with the P-N junction formed therein.

10. A radiation detector according to claim 9 wherein saidradiation-sensitive area is disposed substantially perpendicular to thelengthwise direction of said blood channel and directly contacts bloodflowing through said blood channel.

2. A radiation detector according to claim 1 wherein said semiconductorelement has a P-N junction and said radiation-sensitive area is disposedadjacent to and along a surface of said semiconductor element.
 3. Aradiation detector for medical use according to claim 2 wherein thesurface of the radiation-sensitive area is positioned substantially inparallel with the lengthwise direction of said blood channel, anddirectly contacts blood flowing through said blood channel.
 4. Aradiation detector according to claim 1 wherein the outer surface of thewall section of said detection member is dimensioned to contact theinner wall of the blood vessel into which it is adapted to be inserted.5. A radiation detector according to claim 1 wherein said detectionmember includes a support member having said blood channel formedtherein and wherein said semiconductor element is disposed within saidblood channel and is supported by said support member so that saidradiation-sensitive area directly contacts blood flowing through saidblood channel.
 6. A radiation detector according to claim 5 wherein saidsemiconductor element comprises a rectangular thin semiconductor elementhaving a P-N junction formed substantially adjacent to and in parallelwith the surface thereof, the radiation-sensitive area of saidsemiconductor element being the surface thereof parallel to said P-Njunction, said semiconductor element being positioned so that saidradiation-sensitive area is substantially in parallel with thelengthwise direction of said blood channel.
 7. A radiation detectoraccording to claim 1 wherein the outer circumferential wall section ofsaid detection member is formed by said semiconductor element and saidblood channel is formed in the semiconductor element itself, the outersurface of said wall section being dimensioned to contact the inner wallof the blood vessel into which said detection member is adapted to beinserted.
 8. A radiation detector according to claim 7 wherein saidradiation-sensitive area is disposed substantially perpendicular to thelengthwise direction of said blood channel and directly contacts bloodflowing through said blood channel.
 9. A radiation detector for medicaluse according to claim 7 wherein said blood channel is a grooved channelformed by cutting out a part of the semiconductor element body inwardlyfrom the outer circumferential wall section thereof, saidradiation-sensitive area comprising the surface of the semiconductorelement body disposed adjacent to and in parallel with the P-N junctionformed therein.
 10. A radiation detector according to claim 9 whereinsaid radiation-sensitive area is disposed substantially perpendicular tothe lengthwise direction of said blood channel and directly contactsblood flowing through said blood channel.